@ Chris Scott, Metro-man
It seems then that the MTOW on the latest A320s has grown to the point where manoeuvre load alleviation is beneficial; augmented by the fact that sharklets will pull the wing centre of pressure outwards.
If, as seems likely, they have followed the A340 system principles, then the spoilers will not start to deflect until the aircraft gets to about 2g. That being so, and given that spoiler deflection is the last thing you want if you are looking for enhanced performance, the increased weight at max. altitude on the sharklet equipped aircraft is not going to be anything to do with load alleviation.
Without knowing anything about the engines fitted one cannot be sure exactly where the improvement comes from, but on the face of it a 3% increase in L/D from sharklets is not unreasonable.